COMEDK202510 May 2025Morning ShiftMathematicsDifferential EquationsActual
The solution of (x+ y) d y+y d x=0 when y(0)=1 is
Options
- Ax y+y y+1=0
- Bx y=y y-y-1
- Cy(x+1+ y)-1=0
- Dy(x-1+ y)+1=0
Correct answer
D. y(x-1+ y)+1=0
Step-by-step solution
The given differential equation is (x + y) dy + y dx = 0 . Rearranging the terms, we get y dx + (x + y) dy = 0 , which can be written as y dx + x dy + y dy = 0 . This is equivalent to d(xy) + y dy = 0 . Integrating both sides, we have d(xy) + y dy = C . Using integration by parts for y dy , we get y y - y 1 y dy = y y - y . Thus, the general solution is xy + y y - y = C . Given the initial condition y(0) = 1 , we substitute x = 0 and y = 1 into the general solution: 0(1) + 1 (1) - 1 = C 0 + 0 - 1 = C C = -1 . Subst